1. Field of the Invention
The present invention relates to a plasma display panel, and more particularly to a method and an apparatus for calculating an optimal Average Picture Level (hereinafter referred to as an “APL”) and to a plasma display capable of enhancing a display quality using the same.
2. Description of the Related Art
A plasma display displays a picture using the visible ray generated from a phosphorus material when the phosphorus material is excited by the ultraviolet rays generated by a gas discharge. The plasma display has advantages that it is thinner and lighter than a cathode ray tube (CRT) which has been a display means mast widely used so far and that it is possible to be made into a high definition screen and bigger in size.
The plasma display is driven with time division scheme wherein one frame is divided into several sub-fields that have different light emission frequency, in order to realize the gray level of a picture. Each sub-field is divided again into a reset period for generating a uniform discharge, an address period for selecting discharge cells and a sustain period for realizing gray levels depending on a discharge frequency. For instance, in the event that it is desired to display a picture with 256 gray levels, a frame period 16.67 ms corresponding to 1/60 second is divided into eight(8) sub-fields. In addition, each of 8 sub-fields is divided again into the reset period, the address period and the sustain period. Herein, the reset period and the address period are identically repeated for each sub-field, but on the other hand, the sustain period and the discharge frequency thereof are proportionally increased depending on the number of sustain pulses at the rate of 2n (where n=0, 1, 2, 3, 4, 5, 6, 7) in each sub-field. In this way, since the sustain period becomes different in each sub-field, it is possible to realize the gray level of a picture.
In such a plasma display, luminosity is decided in accordance with the number of sustain pulses. Accordingly, if the number of the sustain pulses are same in each sub-field in case that average luminosity is either lighter or darker, there may arise various problems such as a deterioration of picture quality, excessive power consumption and a damage of a plasma display panel (PDP) due to a non-uniform of average luminosity. For instance, a contrast property may be deteriorated in case that the number of the sustain pulses is set less for every input image. Moreover, in case of setting the number of the sustain pulses more for every input image, the luminosity and the contrast property may be improved even in dark images, but the PDP may be damaged because of increasing the power consumption and the temperature of the PDP. Accordingly, it is needed to appropriately adjust the number of the sustain pulses depending on the average luminosity of the input images. To this end, the plasma display includes a circuit for controlling the number of the sustain pulses in accordance with an APL.
Referring to FIG. 1, there is shown a block diagram representing a related art plasma display. The plasma display includes a gain controller 12 connected between a first reverse gamma corrector 11A and a data aligner 15, an error diffuser 13, a sub-field mapping unit 14, and an APL calculator 16 connected between a second reverse gamma controller 11B and a waveform generator 17.
The first and the second reverse gamma correctors 11A and 11B linearly change brightness for a gray level value of image signals by reverse gamma correcting digital video is data RGB supplied from input lines.
The gain controller 12 functions to adjust gains of the digital video data corrected by the reverse gamma corrector 11A by the amount of effective gains.
The error diffuser 13 adjusts minutely a brightness value by diffusing quantization errors of the digital video data RGB provided from the gain controller 12 throughout adjacent cells. To this end, the error diffuser 13 divides the digital video data into an integer portion and a decimal portion and multiplies the latter by Floid-Steinber's coefficient.
The sub-field mapping unit 14 maps the digital video data provided from the error diffuser 13 to sub-field patterns stored in advance and provides the mapped data to the data aligner 15.
The data aligner 15 provides the digital video data input from the sub-field mapping unit 14 to the data driving circuit of a plasma display panel (hereinafter referred to as a “PDP”) 18. The data driving circuit is connected to data electrodes in the PDP 18, latches the digital video data provided from the data aligner 15 by every one horizontal line, and then provides the latched data by one horizontal period unit to the data electrodes in the PDP 18.
The APL calculator 16 detects by frame unit an average brightness, i.e., APL, for the digital video data RGS input from the second reverse gamma corrector 11B and outputs information on the number of sustain pulses (NSUS) corresponding to the detected APL. For instance, the APL is divided into 256 steps from 0 to 255 assuming that input digital video data is of 8-bit.
The waveform generator 17 generates a timing control signal in response to the information on the number of sustain pulses from the APL calculator 16 and provides it to a scan driving circuit and a sustain driving circuit not shown in FIG. 1. The scan driving circuit and the sustain driving circuit provide sustain pulses to scan electrodes and sustain electrodes in the PDP 18 in response to the timing control signal provided from the waveform generator 17. Generally, a pixel in a PDP includes a set of red, green and blue sub-pixels.
If each red, green and blue sub-pixel is manufactured with the same size, it is difficult to optimize a white balance and a color coordinate of the plasma display without using a particular circuit due to the difference of the unique saturation property of red, green, and blue phosphorus materials. In recent, a PDP of the asymmetric cell configuration wherein the red, green and blue sub-pixels are made to have different sizes, respectively is suggested so as to correct the white balance and the color coordinate.
However, since the conventional method of calculating an APL is made on a condition that all the sub-pixels have the same sizes as mentioned above, an optimal AFL cannot be calculated in the PDP based on the asymmetric cell configuration.